Milling machines and similar surface cutting machine tools include a built in work table, that is, a planar surface on which work pieces are securely and accurately mounted, usually in various types of work holders. The work mounting surface of the work table includes anchoring and alignment structures for the secure and accurate mounting of work pieces to be ready for being machined. The work table of an exemplary milling machine, the Bridgeport® Mill, includes T-slots formed therein, i.e., channels that resemble inverted letters-T's, which run along the length of the work surface. The T-slots accept a variety of keys and bolts, for the precise alignment and fastening of work piece holders to the work surface. Similar work tables are also included in other similar machines such as CNC machining centers.
In a typical milling machine, a work piece is affixed to a built in work table and operated upon by a tool mounted in a motor driven quill, which extends downward from a head. The head is held over the work piece by an overarm, which extends from an upright column. The work table is mounted upon a knee, and can be moved vertically, toward or away from the head, by travel of the knee along a vertical track (not shown) and is traversed past the tooling during machining.
A problem inherent in such machines is the limited vertical travel of the work table. The work table often cannot be lowered sufficiently to accommodate very tall work pieces beneath the head, and cannot be raised sufficiently to bring very short work pieces into the range of an overhead mounted tool.
One way to solve the problem of insufficient work table travel is to alter the height of the column that supports the head. This requires disassembly and reassembly of structural elements of the milling machine. This solution is time consuming and requires much effort. In the case of Bridgeport® Mill, this is done by detaching the overarm and head from the column; mounting a donut shaped spacer (S in FIG. 1) atop the column; and mounting the overarm upon the spacer. Because the overarm supports a heavy motor drive and transmission, the addition or removal of a spacer is a task that requires a hoist and multiple operators, and can take several hours to complete. For this reason once a spacer has been installed and the job is completed, it is generally simply left in place awaiting the next too tall work piece.
This is because the adjusted height state of the machine necessitates the use of extended tooling to reach a short or normal sized work piece. Extended tools are less rigid and stable than corresponding tools of normal length and their use is usually avoided if possible. Another drawback is that, when the head is articulated to direct a tool toward an edge of the work table; even an extended tool may not reach the most peripheral areas of the work surface which allows the machine to be quickly and easily restored to its original capabilities. As a result, once a spacer has been installed, the machine in question is often only used for jobs involving very tall work pieces, and sits idle most of the time.
Work-holding accessories have been used that are attachable to the work table of a milling machine, and most them inherently provide some elevation to a work piece but do not restore a modified machine to its normal capabilities.
For example, several devices mountable upon the work table of a milling machine are disclosed in a web site posted by an author known as John 5293 (http://johnfsworkshop.org/home/links-to-other-pages/the-milling-machine/the-milling-machine-workholding/milling-machine-workholding-tilting-devices/). These devices provide angled surfaces for the attachment of work pieces, and they necessarily also elevate the work pieces above the work surface of the work table. One of the devices is a wedge, depicted in FIG. 427X of John 5293. Although it is simple in construction, and easily handled and mounted, its fixed, sloped upper surface tilts a work piece as well as elevates it. Alignment and anchoring structures, such as T-slots, are not present on the surface of the wedge. Furthermore, the wedge includes no means of stable attachment to a work table.
Other devices disclosed by John 5293 include a tilting table (FIGS. 40X and 551X), and a sine table (FIG. 38X), which designed to provide work surfaces set at precise angles relative to a work table. These devices do accommodate fastening hardware, and their upper surfaces do replicate the T-slots of the work table. The tilting table and sine table are, however, of heavy and complex construction. They do not mount quickly or simply, because their angling mechanisms must be laboriously adjusted to obtain a work surface parallel to the surface of the work table 28.
Another complex accessory that requires angular adjustment is disclosed in U.S. Pat. No. 6,230,070 to Yodoshi. Yodoshi discloses a positioning device including a rectangular base, which is affixable to the work table of a mill machine, and a rectangular mounting member rotatably mounted upon the base. The Yodoshi device does anchor firmly to a work table, but it blocks access to the anchoring and alignment structures of the worktable, and it provides no surface structures to replace them.
U.S. Pat. No. 2,533,753 to Armitage, et al., discloses work-holding fixtures that can be slid along the work table of a milling machine. These fixtures do elevate a work piece and require no angular adjustment prior to use. They do not however, replicate the surface features of the worktable. Instead, they include specialized holders for particular work pieces.
None of these prior art accessories allow quick restoration of the original capabilities to elevate a work piece above the work table of a milling machine.
It is an object of the present invention to provide an arrangement and method enabling a height modified milling machine or the like which enables a quick change to and from a normal machine to a height increased modified machine conveniently to quickly accommodate very high work pieces while being able to be quickly and easily restored to enable normal operation.